Over the past decade I have wasted my money, time and time again on worthless optics mounts. ARMS, GG&G, BOBRO along with the worthless thumb screw mounts that come on ACOG and EOTech plague the shooting community with mounts that fail to perform. Half the problem is the so called “Mil Spec” rail we mount our optics to. Even though the rail is suppose to be a specific size there is often a small variance allowed when these rails are manufactured. Then you have rails that wear down after repeated use of the rail that can wear enough of the surface down to change the size of the rail. The other half of the problem is the mount does not address the varying size of the rail. In my experience Larue Tactical, American Defense Mfg and Global Defense Initiatives (GDI) are the only companies that have addressed this issue. Though American Defense missed the mark with some substandard parts, namely the springs and allowing a drastic forward and aft movement of their mounts. This leaves shooters with Larue and GDI. GDI is a fairly new company having been around since 2002. Then there is Larue. Anyone who carries a long gun as part of their job or those who are serious about shooting know Larue Tactical. Larue Tactical has been a mounting solution staple for years though I truly think GDI is bringing some serious competition to the market.
GDI’s CMC-OSM (Optical Sight Mount) is a mounting solution for the Aimpoint Comp M2 (CCO) & M3. Prior to using this mount I would only trust the Larue Tactical M68/CCO mount. GDI offers three mount options for the M2/M3, Standard Co-witness, lower 1/3 Co-witness and lower 1/3 Co-witness RASII compatible. Mine is the CMC5-OSM which is the standard co-witness. According to GDI’s web site,
http://www.gdiengineering.com/store/products/cmc-osm-optical-sight-mount.html , the mount is CNC machined aerospace grade aluminum with a MilSpec type III hardcoat anodize and it retails for $245.
The mount comes in this cool pouch with loctite 242, torx key, spare torx screw and laminated instructions that are dummy corded to the pouch. It is obvious the packaging has grunts in mind with the handy pouch that can store all sorts of easy to lose items and the spare torx screw gave me a sense of relief because I always manage to drop and lose these screw when mounting optics. The instructions are easy to follow and being on a laminated card will last for years.
I have been running the mount for about two months with at least a dozen live fire ranges, three training exercises and two operations. Day to day it functions just as I knew it would. It retains zero despite being bumped around and abused, I really don’t see continuous live fire as a concern, though time will tell. The first thing I noticed when I started using this optic was how easy it is to mount the optic. The ring is a typical scope ring and is a no brainer to mount. One thing I don’t like about the Larue Tactical CCO mount is the ring clamps side to side rather than top to bottom. It isn’t a huge deal but when you end up mounting a couple dozen optics you begin wondering why the Larue is a side to side clamping ring vs the traditional scope ring.
GDI seems to put more effort into how the mount clamps onto the rail. The Auto Locking Quick Detach (ALQD) Lever sits on the ejection port side (right side) of the weapon. I think this benefits the right handed shooter in keeping the locking lever away from all the gear strapped to the front of your body. The lever is also auto locking so if it does snag on something the lever isn’t moving. The lock clamp or portion of the clamp that is tightened to the rail is 7/8 “ by my measurement compared to Larue Tactical CCO mount that is somewhere between 7/16” and ½” though it is hard to tell where the Larue actually starts biting/clamping the rail.
Mounts unlocked. Larue on the left, GDI on the right
The genius of the GDI mount is its ability to easily adjust to any Mil Spec M1913 rail with only a flat head screwdriver. To adjust the tension simply open the ALQD, incrementally adjust 1/16 -1/8 turn until effective resistance is met when closing and locking the ALQD lever. I find this a valuable attribute whether I am loaning the optic to a student or team mate who needed to borrow an optic on a training day, switching an optic from one weapon to another or showing a student how to set up their optic. To me this method is easier than dealing with the nut on the Larue lever. With the nut you need a tool that is not always common on the range or in the field and those who chose to try to adjust with a multi-tool they tend to round the edges and have difficulty tightening them properly.
GDI adjustment screw
Return to zero is a characteristic I think is vital to any weapon/optic relationship. For those who may not under stand the term, “return to zero” I am talking about removing the optic/mount as one unit, return it to the same location on the weapon rail and the weapon should maintain the original zero with out any adjustments. With out putting the weapon in a vise to take the human error out I found this difficult to accurately measure. A few years ago at Shot Show I got to read the testing report GDI had done on their RCOM-ACOG mount and it showed a .01MOA deviation. GDI’s web site states the same .01MOA deviation for return to zero. I attempted to test this on my own with a Remington 700 (223), RRA M4 and a RRA/Noveske SPR. Here is how I tested each weapon with the mount.
Thjis test was done with a GDI and Larue Tactical Mount
Remington 700 at 100 yards on 3inch dot
M4 at 50 yards on 1.5 inch dot
SPR at 75 yards on 3.5 inch dot
I fired (6) 5rd groups from the prone and off an Atlas bipod and TAB Gear rear bag getting off the rifle between each group. This was to show that the shooter, weapon, optic/mount and ammo were all tracking.
Then I fired (6) 5rd groups in the same manner but after getting off the rifle I would remove the optic and then remount prior to firing the next group. This was to identify any shift in zero. What I found was the Rem 700 test at 100 yards was too difficult and had more human error than equipment error. This was due to the difficulty acquiring a consistent sight picture at 100 yards on a 3 inch dot with a 2moa reticle. The M4 at 50 yards showed some error in the Larue mount with a few groups going approximately 3/8 inch high, I did not detect a change in the GDI mount. The SPR test at 75 yards seemed to be the best of both worlds for testing. I observed no change for the GDI but I did have a high shift for the Larue and then one group shifted high right. The shift on the Larue was approximately 3/4 inch. This was by no means a scientific test but it is hard to ignore the shift on the Larue and no shift on the GDI.
Larue groups with out taking optic off, second picture is the groups with the optic removed and returned to the weapon between groups. The odd ball fliers that are marked were from me not following through on the trigger and the weapon bump firing. The SPR trigger is way too light.
GDI groups. First target the optic stayed on, second target pic the optic was removed and returned between groups. Again, the odd ball flier was me not following through.
The GDI is more expensive but I prefer the GDI mount for the following reasons.
Lever placed on the right side of the weapon.
Locking lever is the most secure and positive on the market.
Return to zero ability.
Easily adjusts for worn out or out of spec rails.
As I proofread this I noticed it appears to be a Larue bashing review. In no way do I think Larue makes substandard products. They are leagues above GG&G, BOBRO and the standard mounts that typically come optics. I just see GDI as bringing some serious innovation to the market and pushing the bar that much higher. GDI being another great company staying with American Made and veteran owned.
I also picked up a T-1 mount and PROM (Precision Rifle Optic Mount) from GDI. I am still working with them and forming opinions. More to come on those mounts later.
